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1.
Jennifer Pincin Michael J. Wilberg Lora Harris Angel Willey 《Estuaries and Coasts》2014,37(4):791-800
Maryland’s coastal bays provide habitat for juveniles of many commercially and recreationally important species of shellfish and finfish. Since 1972, the Maryland Department of Natural Resources has conducted the Maryland Coastal Bays Trawl and Seine Survey to monitor the populations of key species. The survey has undergone substantial spatial and methodological changes affecting the interpretation of simple indices of abundance. We developed generalized linear models to standardize the indices of abundance of five commonly caught fish species: Atlantic menhaden Brevoortia tyrannus, weakfish Cynoscion regalis, spot Leiostomus xanthurus, bay anchovy Anchoa mitchilli, and summer flounder Paralichthys dentatus. Density declined significantly since 1972 for menhaden, bay anchovy, and spot in at least one region within the coastal bays. The northern bays had significantly higher densities than the southern bays for all species. Changes in abundance indices of the five species examined were not related to sea grass coverage, temperature, salinity, nitrogen-to-phosphorus ratios, and other habitat variables but were likely a result of stock-wide recruitment processes. 相似文献
2.
We examined fish assemblages in tidal salt marsh creeks in Delaware Bay in order to evaluate their response to treatment forPhragmites removal following initial treatment in 1996. In Alloway Crrek, a tributary to Delaware Bay, reference creeks draining marsh of untreatedPhragmites or naturally occurringSpartina were compared with creeks in marshes treated forPhragmites removal. These reference and treated creeks occur in close proximity and share many characteristics including salinity, temperature, dissolved oxygen, and turbidity, although creeks inPhragmites sites differed slightly in bathymetry. We analyzed a time series of otter trawl collections (22 monthly sample periods from 1999 to 2001) for differences in juvenile fish assemblage among creeks with different vegetation history. Periodically, young-of-the-year (YOY) and age 1+ white perch (Morone americana), YOY spot (Leiostomus xanthurus), YOY Atlantic menhaden (Brevoortia tyrannus), and other species were relatively more abundant atPhragmites sites, but other dominant species were preiodically abundant at all sites. Among-treatment differences based on principal response curves analysis accounted for about 19% of the total species variation, but differences varied widely among sample periods and there is little or no indication of a trend over the 3-yr period. Larger collections were often associated with subtidal structure, which was more common atPhragmites sites and potentially represents a sampling artifact. Assemblages of creeks with differing vegetation history differ weakly but recognizably, suggesting slow or little response to treatment, at least based on otter trawl collections in subtidal marsh creeks.
相似文献3.
Interactions between pairs of numerically dominant species collected at inlet and creek shorezone and channel habitats within a high salinity estuary in northeastern South Carolina were examined using two-way contingency tables and binomial tests. Of the significant species interactions, over 71% were positive and these primarily occurred within shorezone habitats. The strongest positive interactions were between young-of-the-year spot (Leiostomus xanthurus) and blue crab (Callinectes sapidus) juveniles in both shorezone habitats, and between striped killifish (Fundulus majalis), white mullet (Mugil curema), and striped anchovies (Anchoa hepsetus) in the inlet shorezone habitat. One of the most positive species associations in channel habitats was between the bay anchovy (Anchoa mitchilli) and the Atlantic brief squid (Lolliguncula brevis). These positive relationships between species may be explained by one species enhancing the habitat for another, both species responding to similar environmental conditions, cooperative social interactions such as mixed schooling, or the attraction of predators to prey. Negative interactions were found between schools of Atlantic silversides (Menidia menidia) and striped killifish in the inlet shorezone and between schools of Atlantic silversides and bay anchovies in the creek shorezone. Schools of Atlantic silversides may either displace or compete with other common shorezone species. Positive and negative interactions suggest that relationships between some species pairs did not occur randomly within certain habitats and may have contributed to the organization of the estuarine nekton community. Differences in the strengths and direction of interactions of certain species pairs among habitats and seasons were probably related to the differences in the physical characteristics of those habitats and/or changes in the relative abundance of dominant species and life stages over time. 相似文献
4.
Synoptic ichthyoplankton sampling was conducted on two transects, one on either side of Beaufort Inlet, North Carolina, during the winter immigration season of seven ocean-spawned, estuarine-dependent fishes;Brevoortia tyrannus (Atlantic menhaden),Leiostomus xanthurus (spot),Micropogonias undulatus (Atlantic croaker),Lagodon rhomboides (pinfish),Paralichthys albigutta (Gulf flounder),P. dentatus (summer flounder), andP. lethostigma (southern flounder). Densities and lengths of larvae were significantly different among sampling dates, with distance offshore, and between sides of the inlet. Flood-tide stage had minimal effect on larval densities and lengths except forP. albigutta andP. lethostigma. Changes in larval densities with distance offshore were not coherent among species; densities ofB. tyrammus increased offshore whereas densities of the other species decreased offshore. Average larval densities on a sampling date were coherent among species. Patterns in larval lengths were also coherent among the four non-flounder species. Larval densities outside of Beaufort Inlet were correlated with larval densities inside of Beaufort Inlet. Larval densities outside of Beaufort Inlet were also correlated with the north component of the wind, nearshore water temperature, and distance to the mid-shelf front. Differences in larval density across the inlet were significantly correlated with the east component of the wind. The patterns in larval densities outside of Beaufort Inlet were complex and apparently influenced by both the physical processes that supply larvae to the nearshore region and nearshore physical dynamics. 相似文献
5.
To determine if toxaphene residues in edible fish tissue decreased after removal of contaminated sediments from an estuarine
site in 1999, 51 composite samples representing six finfish species were collected in 2001 and analyzed using gas chromatography
with electron capture and negative ion mass spectrometric detection. The grand mean total toxaphene residue concentration
on a wet weight basis (ΣTOXwet) was 1,400 ± 3,500 ng g−1 (range: < 18 to 18,000 ng g−1) and was positively correlated with extractable lipid. On a lipid basis, the mean ΣTOXlip was 26 ± 33 μg g1, which decreased with increasing distance from the study site. Although benthically-oriented species, such as spot (Leiostomus xanthurus) and striped mullet (Mugil cephalus), exhibited higher mean ΣTOXwet than those of higher trophic level fish, mean ΣTOXlip were not significantly different among species. The grand mean ΣTOX for 2001 was 3.8 (wet) and 2.6 (lipid) times less than
corresponding preremedial action (1997) concentrations, suggesting that bioavailable toxaphene residues in this system have
been reduced. Forage species, such as croaker (Micropogonias undulatus), mullet, and spot, preferentially accumulate toxaphene residues in this system and may serve as vectors of organochlorine
contaminants in the estuarine and coastal ocean food web. 相似文献
6.
We assessed fish assemblage stability over the last half century in Lake Pontchartrain, an environmentally degraded oligohaline
estuary in southeastern Louisiana. Because assemblage instability over time has been consistently associated with severe habitat
degradation, we attempted to determine whether fish assemblages in demersal, nearshore, and pelagic habitats exhibited change
that was unrelated to natural fluctuations in environmental variables (e.g., assemblage changes between wet and dry periods).
Collection data from three gear types (trawl, beach seine, and gill nets) and monthly environmental data (salinity, temperature,
and Secchi depth) were compared for four collecting periods: 1954 (dry period), 1978 (wet period), 1996–1998 (wet period),
and 1998–2000 (dry period). Canonical correspondence analysis (CCA) revealed that although the three environmental variables
were significantly associated with the distribution and abundance patterns of fish assemblages in all habitats (with the exception
of Secchi depth for pelagic samples), most fish assemblage change occurred among sampling periods (i.e., along a temporal
gradient unrelated to changing environmental variables). Assemblage instability was the most pronounced for fishes collected
by trawls from demersal habitats. A marked lack of cyclicity in the trawl data CCA diagram indicated a shift away from a baseline
demersal assemblage of 50 yr ago. Centroid positions for the five most collected species indicated that three benthic fishes,
Atlantic croaker (Micropogonias undulatus), spot (Leiostomus xanthurus), and hardhead catfish (Arius felis), were more dominant in past demersal assemblages (1954 and 1978). A different situation was shown for planktivorous species
collected by trawls with bay anchovy (Anchoa mitchilli) becoming more dominant in recent assemblage and Gulf menhaden (Brevoortia patromus) remaining equally represented in assemblages over time. Changes in fish assemblages from nearshore (beach seine) and pelagic
(gill net) habitats were more closely related to environmental fluctuations, though the CCA for beach seine data also indicated
a decrease in the dominance ofM. undulatus and an increase in the proportion ofA. mitchilli over time. The reduced assemblage role of benthic fishes and the marked assemblage change indicated by trawl data suggest
that over the last half century demersal habitats in Lake Pontchartrain have been impacted more by multiple anthropogenic
stressors than nearshore or pelagic habitats. 相似文献
7.
Larval fishes were sampled weekly from late fall to early spring in the Newport River estuary just inside Beaufort Inlet, North Carolina. Quantitative samples were taken during darkness at mid-flood tide with paired 60-cm bongo nets (505-μm mesh). Larvae of 22 species from 15 families were collected. Seventy-seven percent of the species and 97% of the individuals were fishes that had been spawned on the continental shelf and had immigrated to the estuary. In descending order, the five most abundant species, accounting for 90% of the individuals, were spot (Leiostomus xanthurus), Atlantic croaker (Micropogonias undulatus), Atlantic menhaden (Brevoortia tyrannus), pinfish (Lagodon rhomboides), and speckled worm ell (Myrophis punctatus). Most species immigrated through-out the winter and into spring, but there were distinct patterns in their temporal abundances. 相似文献
8.
The seasonal occurrence and relative abundance of larval and juvenile fishes, particularly members of the family Sciaenidae, from a Virginia Atlantic coast estuary were determined from ichthyoplankton and otter trawl collections made from March 1979 to March 1980. The larvae of 19 species in 14 families were identified in the ichthyoplankton. Larvae of the engraulid, Anchoa mitchilli (bay anchovy), and the atherinid, Menidia menidia (Atlantic silverside), dominated the samples and made up 13 and 22%, respectively, of the 9,440 larvae collected. Peak occurrence of all larvae was from May to August. The juveniles of 28 species in 19 families were identified from otter trawl collections. Juvenile sciaenids numerically dominated the trawl collecions and made up 68% of the trawl catch. Juvenile density peaked during September through December. 相似文献
9.
J. C. Joyeux 《Estuaries and Coasts》1999,22(4):889-904
The larvae of winter spawning fishes immigrating through Beaufort Inlet into the Pamlico Sound estuarine system (North Carolina, United States) were passively sampled during 14 flood tides and nine of the following ebb tides. Five taxa were abundant in the catches. Pelagic species were represented by Atlantic menhaden, Brevoortia tyrannus. Nonpelagic taxa were represented by Atlantic croaker, Micropogonias undulatus, spot, Leiostomus xanthurus, pinfish, Lagodon rhomboides, and flatfishes of the genus Paralichthys. The sampling was continuous and the sample duration varied between 4 min and 32 min. The longest samples furnished the most accurate and precise estimates of the mean tidal abundance. Sampling 10 min each hour of the tide was the most efficient protocol for determining the mean tidal abundance. The abundance patterns was shown to differ according to the pelagic or nonpelagic behavior of the larvae. Analyses suggested the nonpelagic taxa rely on astronomical tides and vertical migrations synchronous with the direction of the tide flow to be transported upstream in the estuary. These larvae were not dependent upon the strength of the tide to penetrate the inlet. In contrast, menhaden larvae seemed to rely primarily on strong food tides to enter the estuarine area, probably because the vertical positioning of the species within the water column is not dependent upon the direction of the tide. However, if larvae were present outside of the inlet, strong flood tides indiscriminately brought pelagic and nonpelagic species into the estuary. 相似文献
10.
We examined the community structure of fish and selected decapod crustaceans and tested for within estuary differences among habitats at depths of 0.6 m to 7.9 m, in Great Bay and Little Egg Harbor in southern New Jersey. Several habitat types were identified a priori (e.g., eelgrass, sea lettuce, and marsh creeks) and sampled by trawl (4.9 m headrope, 19-mm mesh wings, 6.3-mm mesh liner), monthly, from June 1988 through October 1989. Repetitive (n=4) 2-min trawl tows were taken at each habitat type from 13 locations. The fishes and decapod crustaceans collected were typical of other Mid-Atlantic Bight estuaries but varied greatly inseasonal abundance and species. In the years sampled, bay anchovy (Anchoa mitchilli) was the dominant species (50.5% of the total number), followed by spot (Leiostomus xanthurus) (10.7%), Atlantic silverside (Menidia menidia) (9.7%), fourspine stickleback (Apeltes quadracus) (5.9%), blue crab (Callinectes sapidus) (4.6%), and northern pipefish (Syngnathus fuscus) (4.2%). The biota were examined by multi-dimensional scaling (MDS) for habitat associations and “best abiotic predictor” of community structure. Percent silt combined with salinity was the most important abiotic determinant of the faunal distributions among habitats. Temperature was a major factor influencing seasonal occurrence of the biota but had less effect on habitat comparisons. The analysis confirmed the distinct nature of the assemblages associated with the habitats, that is, eelgrass, upper estuary subtidal creeks, channels, and open bay areas. Several species were associated with specific habitats: for example,A. quadracus andS. fuscus with eelgrass, clupeids with subtidal creek stations,L. xanthurus with marsh channels, and black sea bass (Centropristis striata) and spotted hake (Urophycis regia) with sponge-peat habitat. Species richness appeared to be positively related to habitat structural heterogeneity. Thus, the best predictors for these estuarine fish and decapod crustacean assemblages were seasonal temperature, percent silt and salinity combined, and the physical heterogeneity of the habitat. 相似文献
11.
Analysis of polychlorinated biphenyls (PCBs) in selected finfish and shellfish from the estuarine and coastal marine waters of New Jersey reveals variable levels of contamination in different regions of the state. Monitoring surveys conducted by the New Jersey Department of Environmental Protection during the last two decades indicate that biota from the northeast region are the most severely contaminated with PCBs. Early monitoring in the 1970s showed that as much as 75% of the finfish and 50% of the shellfish analyzed for Aroclor 1254—the most persistent and toxic mixture of PCBs—contained detectable levels of PCB in their edible flesh. The American eel (Anguilla rostrata), bluefish (Pomatomus saltatrix), striped bass (Morone saxatilis), white catfish (Ictalurus catus), white perch (M. americana), and blue crab (Callinectes sapidus) exhibited high PCB levels in 1981–1982, generally approaching or exceeding the United States Food and Drug Administration action level of 2 ppm fresh weight for these organisms. PCB contamination in finfish and shellfish collected during survey periods of 1986–1987 and 1988–1991 was consistent with the previous years' data showing the northeast region of the state to be the most severely contaminated. Despite decreases in contaminant levels in some species (e.g., striped bass) and regions, results of the most recent survey confirm widespread occurrences of PCBs above background levels in the edible portions of various species from many areas of New Jersey. 相似文献
12.
Peter J. Hanson 《Estuaries and Coasts》1997,20(4):659-676
Multivariate analysis of contaminant data from a multi-year monitoring program demonstrates alterations in the hepatic chemistry of metals in fish exposed to organic contaminants. Metals (Ag, As, Cd, Cu, Fe, Hg, Mn, Ni, Pb, Se, Sn, Zn) and organic chemicals (PCBs, DDTs, chlordanes, dieldrins, PAHs) were measured in liver and associated sediments for winter flounder (Pleuronectes americanus) from 23 sites along the northeast Atlantic coast and for Atlantic croaker (Micropogonias undulatus) from 30 sites along the southeast Atlantic and Gulf of Mexico coasts of the United States. Concentrations of habitat contaminants varied from nil to levels signifying important anthropogenic inputs and thus provided a range in chronic exposures and related contaminant stress levels with which to investigate the response of hepatic chemistry in fish representative of viable populations. The data, analyzed by principal component, principal component regression, and biplot procedures, demonstrated an opposing relationship between micronutrient elements, principally Zn, and exposure to organic contaminants in winter flounder. This relationship was not present in Atlantic croaker that were resident in less contaminated habitats. Based on median concentrations in sediment, exposure of winter flounder to important organic contaminants (polycyclic aromatic hydrocarbons, polychlorinated biphenyls, DDTs) exceeded that for Atlantic croaker by 7 to 50 times. Coincident with depletion of hepatic Zn and Cd in winter flounder was accumulation of Hg and Ag. My results, in agreement with those of others, implicate the negative effects of hepatic detoxification of organic contaminants on metal binding in liver, which can cause depletion of essential elements while contaminant and potentially toxic elements accumulate. 相似文献
13.
The structure of the fish community associated with eelgrass beds in the lower Chesapeake Bay was studied over a 14 month period. A total of 24,182 individuals in 48 species was collected by otter trawl with Leiostomus xanthurus (spot) comprising 63% of the collection, Syngnathus fuscus (northern pipefish) 14%, Anchoa mitchilli (bay anchovy) 9%, and Bairdiella chrysoura (silver perch) 5%. The density and diversity of fishes were higher in vegetated areas compared to unvegetated areas; fishes were more abundant in night collections Fish abundance and species number increased in the spring and early summer as both water temperature and eelgrass biomass increased and decreased in the fall and winter as temperature and eelgrass biomass decreased. Gill netting revealed some of the top predators in the system, especially the sandbar shark, Carcharhinus milberti. The fish community in the Chesapeake Bay was quite different from North Carolina eelgrass fish communities. Most notable was the rarity of the pinfish, Lagodon rhomboides, which may be a very important predator in the structuring of the epifaunal communities. 相似文献
14.
Frances P. Gelwick Senol Akin D. Albrey Arrington Kirk O. Winemiller 《Estuaries and Coasts》2001,24(2):285-296
We described seasonal fish-assemblages in an estuarine marsh fringing Matagorda Bay, Gulf of Mexico. Habitat zones were identified by patterns of fish species abundance and indicator species optima along gradients in salinity, dissolved oxygen (DO), and depth in our samples. Indicators of the lower brackish zone (lower lake and tidal bayou closest to the bay) were gulf menhaden (Brevoortia patronus), bay anchovy (Anchoa mitchilli), silver perch (Bairdiella chrysoura), and spotted seatrout (Cynoscion nebulosus) at salinity >15‰, DO 7–10 mg l−1, and depth <0.5 m. Indicators of the upper brackish zone (lake and fringing salt marsh) were pinfish (Lagodon rhomboides) and spot (Leiostomus xanthurus) at salinity 10–20‰, DO >10 mg l−1, and depth <0.5 m. In the freshwater wetland zone (diked wetland, ephemeral pool, and perennial scour pool), indicators were sheepshed minnow (Cyprinod on variegatus), rainwater killifish (Lucania parva), mosquitofish (Gambusia affinis), and sailfin molly (Poecilia latipinna) at salinity <5‰, DO <5 mg l−1, and depth ≥1 m. In the freshwater channelized zone (slough and irrigation canal), indicators were three sunfish species (Lepomis), white crappie (Pomoxis annularis), and gizzard shad (Dorosoma cepedianum) at salinity <5‰, DO <5 mg l−1, and depth >1.5 m. In brackish zones, seasonal variation in species diversity among sites was positively correlated with temperature, but assemblage structure also was influenced by depth and DO. In the freshwater zones, seasonal variation in species diversity among sites was positively correlated with depth, DO, and salinity, but assemblage structure was weakly associated with temperature. Species diversity and assemblage structure were strongly affected by the connectivity between freshwater wetland and brackish zones. Uncommon species in diked wetlands, such as tarpon (Megalops atlanticus) and fat sleeper (Dormitator maculatus), indicated movement of fishes from the brackish zone as the water level rose during natural flooding and scheduled (July) releases from the diked wetland. From September to July, diversity in the freshwater wetland zone decreased as receding waters left small isolated pools, and fish movement became blocked by a water-control structure. Subsequently, diversity was reduced to a few species with opportunistic life histories and tolerance to anoxic conditions that developed as flooded vegetation decayed. 相似文献
15.
Isaac Wirgin Blake Konkle Mark Pedersen Cheryl Grunwald Jim Williams Simon C. Courtenay 《Estuaries and Coasts》1996,19(4):913-922
Quantification of levels of cytochrome P4501A (CYP1A) gene expression in sentinel species of fishes has been proposed as a management tool to evaluate contamination of aquatic systems. Based on preliminary studies, we hypothesized that differences in CYP1A mRNA inducibility among individuals, populations, or species might lead to spurious conclusions when using this approach in environmental monitoring programs. To address this possibility, we quantitated and compared CYP1A mRNA induction levels in four species of common Atlantic Coast estuarine fish: smooth flounder, hogchoker, striped bass, and Atlantic tomcod, which were treated with model chemicals (beta naphthoflavone (β-NF), or benzo[a]pyrene at 10 ppm) known to induce CYP1A mRNA, or were exposed to contaminated environments. Species-specific CYP1A DNA probes were generated from PCR (polymerase chain reaction) amplification of genomic DNA using conserved oligonucleotide primers, and, along with cloned rainbow trout and Atlantic tomcod CYP1A cDNA probes were used to quantify CYP1A mRNA levels in northern blot analyses. Successful PCR amplification of CYP1A hybridizable DNA fragments was observed for all four species. Results from northern blot analyses showed large differences in CYP1A mRNA induction among species; only Atlantic tomcod exhibited significant induction of CYP1A mRNA for both chemically treated (97-fold) and environmentally exposed fish (34-fold). Significant, although lower, levels of induction were observed in β-NF treated (14-fold) smooth flounder, but not in environmentally exposed smooth flounder. Only low levels (not significant) of CYP1A gene induction were detected in hogchokers and striped bass. We conclude that CYP1A mRNA inducibility differed significantly among fish taxa perhaps due to differences in regulation of gene expression, suggesting that careful selection of sentinel species should be exercised prior to the use of CYP1A mRNA induction in environmental monitoring programs. However, the significance of differences in CYP1A mRNA inducibility in relation to higher level biological endpoints has yet to be determined. 相似文献
16.
Nekton and macrocrustacean population levels and characteristics were studied in two similar tidal marsh creeks. Absolute and area-adjusted data were analyzed to determine variability resulting from daily population fluctuations. Two sampling schemes—intensive 3-d seasonal and periodic 1-d—were examined by constructing probability matrices to compare the accuracy of data comparisons resulting from each scheme. The probability of inaccuracies in comparisons of abundance using nonreplicated sampling schemes ranged from 0% to 100%. Significant differences between consecutive day data were observed for population characteristics such as blue crab (Callinectes sapidus) sex ratios, spot (Leiostomus xanthurus) length-weights, killifish: sciaenid ratios, and killifish: blue crab ratios. These data support the need to account for short-term variability when assessing mobile aquatic fauna abundance in estuarine wetlands. 相似文献
17.
Salinity fluctuation has been proposed as an important determinant of estuarine fish distribution. To test this idea, we compared distribution, behavioral preference and physiological sensitivity of two juvenile estuarine fishes, spot (Leiostomus xanthurus) and croaker (Micropogonias undulatus), with respect to salinity change. In field collections, spot: croaker ratios were positively correlated with salinity variation. Subsequent behavioral observations revealed that croaker tend to cross a 10‰ salinity gradient less often than spot. We proposed that energetic costs of salinity adaptation may be higher for croaker, resulting in the observed avoidance behavior. Oxygen consumption rates over rapid salinity fluctuations showed no significant differences in metabolic response between species, although there was some indication that sensitivity changes with fish size. Apparently, juvenile spot and croaker are well-equipped to withstand extreme changes in salinity. We conclude that environmental factors correlated with salinity change may be responsible for distribution differences between these two abundant species. 相似文献
18.
To better characterize human health risks associated with potentially contaminated seafood, 56 composite samples of edible tissue of several finfish and shellfish species were analyzed for residues of toxaphene using gas chromatography with electron capture and negative ion mass spectrometric detection (GC-ECD and GC-ECNI-MS). Toxaphene in these samples, collected in 1997 near a former toxaphene plant in Brunswick, Georgia, were previously reported as non-detectable using non-selective techniques. Estimated total toxaphene concentrations (ΣTOX) ranged from less than 0.01 to 26 μ g−1 on a wet tissue basis. Smaller, bottom dwelling finfish such as croaker, mullet, and spot exhibited the highest ΣTOX (0.76–26 μg g−1), larger predatory fish including seatrout contained intermediate levels (0.08–4.4 μg g−1), and shellfish (blue crab and shrimp) contained the lowest levels (<0.01 to 0.27 μg g−1). For a given species, samples from the site furthest from the toxaphene plant had lower ΣTOX than samples from the other 3 sites. On a congener specific basis, levels ranged from <0.0025 to 3.5 μg g−1. Congener distributions were, in general, dominated by 2-exo, 3-endo, 6-exo,8,9,10-hexachlorobornane (Hx-Sed) and 2-endo,3-exo,5-endo,6-exo,8,9,10-heptachlorobornane (Hp-Sed), breakdown products of Cl8−Cl10 toxaphene homologs. Other prominent congeners confirmed by GC-ECNI-MS included Parlar numbers 26, 40/41, 42, 44, 50, 62, and 63, as well as several unidentified Cl6−Cl9 homologs. Minor differences in congener distribution among species and sampling locations suggested that exposure regimes and/or intrinsic biotransformation capabilities were not uniform. These results indicate that toxaphene residues were detectable in all species surveyed and at concentrations higher than estimated previously. 相似文献
19.
During 1973 and 1974 seasonal abundance and mean total length of Atlantic croaker,Micropogonias undulatus, were investigated by otter trawl at 33 stations in South Carolina estuaries in relation to bottom salinity and temperature. Relative abundance of Atlantic croaker was measured by catch per unit effort at 3°C temperature intervals and 3‰ salinity intervals. Croaker occurred over a bottom temperature range of 9.0–31.4°C while occurring most abundantly in waters above 24.0°C. No significant correlation between size and temperature was found. Croaker were collected in salinities from 0.4 to 34.4‰. High correlations of size and salinity were evident in 1973 during winter (r=0.79), summer (r=0.82), and fall (r=0.94). In 1974, correlations were significant only during fall (r=0.76). 相似文献
20.
Maintaining proper freshwater and marine inputs is essential for estuarine function. Alteration of freshwater flows into small
tributaries that traverse the upland-estuarine margin may be especially problematic, e.g., by impacting the nursery areas
for juvenile finfish and shellfish. We used stomach contents and stable isotope analysis (δ13C, δ15N) to examine effects of freshwater flow alterations on the trophic ecology of juvenile common snook (Centropomus undecimalis) in four mangrove creeks with different freshwater flow regimes. Diet diversity in less degraded creeks was greater than
in more degraded creeks, and the importance (by % mass) of the top three preys was disproportionately higher in the more degraded
creeks. Stable isotope measures of trophic diversity corroborate these trends, suggesting higher intraspecific trophic diversity
in less degraded creeks. The difference in diet diversity of juvenile snook may be an indicator of an overall change in ecosystem
function and these shifts in food web structure may affect the rate that juveniles of this and other species with similar
habitat requirements successfully join the adult population. 相似文献